Control regulators or throttling valves of the type that incorporate deformable elastomeric diaphragms or liners that operate by pressure differentials on their two sides to variably uncover a plurality of orifices, e.g., slots, in a baffle positioned between an upstream inlet and a downstream outlet in a flowpath are well known in the art. The operating pressure is referred to as a pilot pressure and is changeable to control the operating position of the liner. Such valves may, for example, be used for controlling the flow of a variety of fluids and gases and, because of their throttling nature, often operate in a partially open position with a substantial differential between the upstream and downstream pressures. While such valves have, in general, rendered satisfactory service, they are not without problems. In gas applications in particular, the flow velocity may create icing conditions on the diaphragm and give rise to problems in shut-off.
The flexible liners are also subject to stretching. Under certain operating conditions the diaphragms may be "pinched" or folded over upon themselves which is detrimental to the life of the liner and proper functioning of the valve.
The baffle generally comprises a frustroconical shaped grill containing slot shaped apertures that are progressively covered and uncovered by the diaphragm as it is "rolled" into contact therewith. The portion of the slots that are uncovered by the diaphragm determines the flow rate through the baffle. Difficulties in some designs have resulted from uneven rolling of the diaphragm. A backup "nose piece" is often included to provide a stationary surface against which the diaphragm may rest to assist in controlling its movement during unrolling to minimize the above mentioned pinching and foldover. The slot configuration for the grill holes is very common, although circular or other shaped holes may also be used.
Another problem encountered with the rolling diaphragm is the tendency of the liner to be extruded into the slots of the frustroconical grill by action of the operating pilot pressure against the diaphragm when the valve is closed or partially closed. A notable deficiency is the lack of any readily available means for indicating the amount that the valve is open for flow. Also, the valves are generally cylindrically shaped and designed to be clamped in the pipeline by suitable flanges and bolting. This has rendered servicing of the valve inconvenient in many installations.